This research proposal seeks to delineate the mechanisms of action of luteotropic agents, LH and PRL, on steroidogenesis in the corpus luteum. Emphasis will be placed on the use of an in vitro system in which dispersed, homogeneous luteal cells will be examined during the continuous or pulsed supply of substrate and/or regulatory agents. Changes in cell function will be correlated with secretion rates of progesterone and 20 alpha-dihydroprogesterone. The following more specific aims are present: 1. To correlate the luteal cell binding of labeled hCG and PRL with steroidogenesis; 2. To study the rates of gonadotropin-receptor dissociation with consideration for hormone internalization and receptor desensitization; 3. To study the utilization of cholesteryl esters of low density lipoprotein as substrate for steroidogenesis by dispersal luteal cells and mitochondria; 4. To study the mechanism of protein kinase stimulation of luteal mitochondria steroidogenesis; 5. To define effects on steroidogenesis of potential activators, e.g., estradiol-17 beta, PGE2, cholera toxin, etc., during perifusion; 6. To define effects on steroidogenesis of potential activators, e.g., estradiol-178, PGE2, cholera toxin, etc., during perifusion; 6. To define effects on steroidogenesis of potential inhibitors, e.g., amino-glutethimide, cytocholasin B, cycloheximide, isoxozole, PGF2 alpha; LH binding inhibitor, etc., during perfusion of luteal cells and mitochondria; 7. To use long term perifusion of luteal cells to initiate luteolysis.